Reversible Electrical Resistance Switching in GeSbTe Thin Films: An Electrolytic Approach without Amorphous-Crystalline
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1071-F09-09
Reversible Electrical Resistance Switching in GeSbTe Thin Films: An Electrolytic Approach without Amorphous-Crystalline Phase-Change Ramanathaswamy Pandian, Bart J. Kooi, George Palasantzas, and Jeff Th. M. De Hosson Department of Applied Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen, 9747 AG, Netherlands ABSTRACT Besides the well-known resistance switching originating from the amorphous-crystalline phase-change in GeSbTe thin films, we demonstrate another switching mechanism named ‘polarity-dependent resistance (PDR) switching’. The electrical resistance of the film switches between a low- and high-state when the polarity of the applied electric field is reversed. This switching is not connected to the phase-change, as it only occurs in the crystalline phase of the film, but connected to the solid-state electrolytic behavior i.e. high ionic conductivity of (Sbrich) GeSbTe under an electric field. I-V characteristics of nonoptimized capacitor-like prototype cells of various dimensions clearly exhibited the switching behavior when sweeping the voltage between +1 V and -1 V (starting point: 0 V). The switching was demonstrated also with voltage pulses of amplitudes down to 1 V and pulse widths down to 1 microsecond for several hundred of cycles with resistance contrasts up to 150 % between the resistance states. Conductive atomic force microscopy (CAFM) was used to examine PDR switching at nanoscales in tip-written crystalline marks, where the switching occurred for less than 1.5 V with more than three orders of resistance contrasts. Our experiments demonstrated a novel and technologically important switching mechanism, which consumes less power than the usual phase-change switching and provide opportunity to bring together the two resistance switching types (phase-change and PDR) in a single system to extend the applicability of GeSbTe materials. INTRODUCTION For the next generation nonvolatile memories, several random access memory (RAM) technologies have been proposed e.g. based on magneto-resistance (MRAM), ferroelectricity (FRAM), phase-change (PRAM) and electrical-resistance (RRAM). Among them, PRAM and RRAM based on electrical resistance switching have been given more focus in recent years as they prove to be promising candidates for the next generation nonvolatile memories. Being the active medium of the proposed phase-change and electrical-resistance based memories, chalcogenide materials are particularly promising and versatile. PRAM is based on resistance switching caused by amorphous-crystalline phase-change and is not voltage-polarity dependent. RRAM, on the other hand, is sensitive to polarity of the applied voltage and is not connected to phase-change. The resistance switching of RRAM is attributed to the electrolytic behavior and/or ionic conductivity of the material in the solid-state. Thus far, the phase-change and polaritydependent resistance switching in chalcogenides were considered independently. For example, numerous compositions
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